The first glyphosate-resistant weed identified in U.S. row crops in 2000, marestail is a dangerous weed. It produces up to 200,000 seeds/plant and grows up to 5-6 feet tall. The seeds are highly mobile, which results in rapid spread.
Marestail usually germinates in fall and spring, but can germinate year-round.
Waterhemp produces up to 1 million seeds/plant and can grow as much as 1 inch/day. The average height is 4-5 feet tall, with some weeds reaching up to 12-feet tall.
The pollen from these weeds can travel ½ a mile or more and because of the cross pollination that occurs, resistance can spread quickly.
Palmer amaranth thrives in reduced-, minimum- or no-tillage systems because it germinates close to the soil surface. It can produce 10,000 to 100,000 seeds/plant and has the potential to overtake the crop due to its rapid growth and aggressive competition.
Palmer amaranth has prolific seed production and germination throughout the season. It has a faster growth rate and is more competitive than other pigweed species, with growth rates approaching 3 inches/day.
When allowed to compete throughout the growing season, Palmer amaranth can create yield losses up to 91% in corn. It can reach 8 feet in height.
Once established, morningglory is very difficult to control with post-emergence applications of herbicides. It competes with corn crops for nutrients and has the potential to reduce yield.
Morningglory can produce up to 500 seeds/plant, and, due to an extremely hard seed coat, some seeds can remain viable in the soil for more than 50 years.
Field research demonstrates that season-long competition from just 2 giant ragweed plants per 110 square feet can reduce corn yield by 13%.
Giant ragweed often grows taller than the crop, sometimes up to 5 feet taller. It can produce up to 5,100 seeds per plant.